Ignitor containing polymeric nf{11 -adducts

ABSTRACT

1. An ignitor composition consisting essentially of 40 to 70 wt. percent of a solid oxygen-oxidizer and a solid NF2-containing polymer in which NF2 groups attached to carbon atoms give the polymer an NF2 content of 40 to 70 wt. percent NF2, said solid oxygen-oxidizer making available oxygen for reaction with carbon constituents and forming N2 gas.

United States Patent 1191 Spenadel et al.

1451 Sept. 24, 1974 IG NITOR CONTAINING POLYMERIC NEZ-ADDUCTS [75] Inventors: Lawrence Spenadel, Fanwood; John C. Reed, Westfield, both of NJ.

[73] Assignee: Esso Research and Engineering Company, Linden, NJ.

[22] Filed: Feb. 28, 1963 [21] Appl. No.: 262,292

52 us. c1 ..149/19.3, 149/20,149/36, 149/89 [51] mm ..C06d 5/06 58 Field 61 Search... 149/19, 20, 36,75, 76, 149/89 [5 6] References Cited UNITED STATES PATENTS 3,441,549 4/1969 Giardiner 149/19 X 3,441,550 4/1969 Zimmerman 149/19 X Primary Examiner-Benjamin R. Padgett EXEMPLARY CLAIM 4 Claims, N0 Drawings IGNITOR CQNIAllSING POLYMERIC NFZ -ADDUCTS This invention relates to an improved ignitor system for a solid propellant. The improved ignitor consists essentially of a mixture of two components, one being a selected solid oxygen-oxidizer and the other an energetic solid polymer which .contains from 40 percent to about 70 wt. percent NF groups linked to carbon atoms, the oxygen-oxidizer being in a proportion of from 40 to 70 wt. percent and the NF -containing polymer being in a proportion of about 60 to wt. percent.

A recurring problem in obtaining high firing efficiency without failure of the propellant grain at low pressures, even under vacuum conditions, has been experienced and has been found to be due to adverse characteristics of the ignitor. in tests of a wide variety of conventional and commercial ignitors, it has been found that a number of them will not ignite under vacuum conditions with simple heating means, a number of them burn too slowly so as to give an ignition delay which results in low firing efficiency of the propellant, while others may burn too energetically or explosively with high gas evolution causing breakup of the propellant grain and splinter burning. Still another defect of some of the conventional ignitors is that they do not contribute to the impulse of the propellant grain and have to be used in excessive amounts.

In accordance with the present invention, the new ignitor developed overcomes the deficiencies aforementioned, particularly in that its ignition can be initiated at low temperatures, even under very low pressures, can be used in smaller amounts in conjunction with a propellant grain and adequately starts the burning of the propellant grain without excessive delay and without over-ignition.

The solid oxygen-oxidizer component suitable for the improved ignitor system in which the other component is an NF -substituted polymer may be selected from the group consisting of ammonium perchlorate, NH CIO hexanitroethane, C (NO hydrazine nitroformate, N H C( NO hydrazine diperchlorate, N H (2HClO and nitronium perchlorate, NO ClO,. These solid oxygen-oxidizers make available a high amount of oxygen for reaction with carbon constituents to form CO and CO while forming N gas, the carbon being present mainly in the NF -containing polymer which furnishes fluorine for reaction with hydrogen to form HF as a combustion product. The resulting reaction of the oxygen'oxidizer with the NF -containing polymer gives a rapid increase of temperature without excessive gas formation.

The suitable NF -containing polymer component is selected from the group consisting of NF adducts of polymers such as polybutadiene, poly(difluoraminoalkyl acrylates), poly(difluoraminoalkyl ether) acrylates, and polyurethanes of poly(difluoraminoalkyl ethers). These polymers have been formed to contain from 40 to 70 wt. percent NF in the form of NF groups linked to carbon atoms.

The polybutadiene-NF adducts have a composition represented by the recurring unit:

in which the subscript x represents on the average of from one to two NF groups linked to carbon atoms in the monomeric unit.

The poly(difluoraminoalkyl) acrylates are represented by the recurring composition formula of polybis(NF propyl acrylate:

and of poly-tetrakis(NF amyl acrylate:

The difluoramino polyethers are represented by 4,5- bis(NF pentene-l oxide:

and l,2,5,6-tetrakis(NF hexene-3 oxide. Such polyethers can be formed with modifiers to have terminal OH groups which, on reaction with acrylating agents, e.g., acrylic acid, form acrylates, and on reaction with diisocyanates or polyisocyanates form the polyurethanes which contain NF groups. The solid polymers have molecular weights above 500 and, generally, in the range of 1,000 to 100,000.

For brevity, the described energetic solid polymers are generally termed solid NF -containing polymers which contain about 40 to wt. percent NF in carbon-to-NF linkages.

To make up the ignitor from the solid oxygenoxidizer and the NF -containing polymer, these solid materials may be mixed as powders of less than 20 mesh size. The solid may be ground or comminuted separately and then mixed in the desired proportions so as to distribute the particles uniformly or homogeneously. The mixed solid particles may be pressed or cast into pellets. The loose mixed powder may be placed in a polyethylene bag or similar kind of container which can then be centered in a rocket nozzle inlet section next to the propellant grain. The pelleted powdered mixture may be placed against the surface of the grain which is to be ignited with an electrical resistance wire contacting the pellets to heat them to their ignition points when electricity is passed through the wire.

There are various ways known in the prior art for affixing the ignitors to the propellant grains and placing the ignitors at or near the surfaces at which firing is to be started. in some instances, a chemical initiator which may be termed a squib or a match has been used to start the burning of the ignitor requiring a higher temperature for ignition, but such systems have not been found as good as the ignitor containing the solid oxygen-oxidizer mixed with an NF -containing polymer provided by the present invention. The autoignition temperature for a variety of conventional ignitors, such as those containing metals like boron, beryllium, aluminum, titanium, magnesium, black powder and solid monomeric oxidizers, have been found to have autoignition temperatures of 260 to 400C. These initiators would not prove satisfactory alone or with other ignitors under vacuum conditions, or have been unsatisfactory in other respects, e.g., create a rapid gas pressure rise which is injurious to the grain.

Comparative ignitor tests were carried out under vacuum conditions as low as about 1 1 inches Hg abs. and 1 inch Hg abs. using a rocket motor containing an end burning grain of standard double base propellant which contains nitroglycerine and nitrocellulose. Under the vacuum conditions, the only ignitor which gave satisfactory ignition was a mixture of 50 wt. percent solid oxygen-oxidizer, such as ammonium perchlorate, and 50 wt. percent of an NF -containing polymer, such as polybutadiene-NF adduct of about 55 wt. percent NF: content. It was demonstrated that the solid oxygenoxidizer mixed with NF -containing polymer could be used to ignite any standard solid propellant as well as the higher energy propellants containing low amounts of binder with solid oxygen-oxidizer, powdered metal fuel and liquid NF -containing oxidizers. It was demonstrated that the amount of ignitor for initiating firing of the propellant grains could be kept as low as 0.05 to 0.2 wt. percent on the total weight of the propellant grain, which is an advantage in raising the lsp (specific impulse) value of the propellant, particularly such propellants having a desired high-energy value with lsp values above 270.

Determinations have been made on the heat generated by the various ignitors and temperatures and pressures developed in the combustion chamber in using the various ignitors, with the ignitors containing a mixture of the solid oxygen-oxidizer, 40 to 70 wt. percent, and NF -containing polymer in a proportion of 30 to 60 wt. percent, without metal fuel. The chamber temperatures reached well into the range of 2,600 to 3,000K. Putting a metal fuel into the mixture drastically reduced the temperature since heat was generated. The heat generated is determined in calories per gram and is preferably of the order of 1,000 to 1,400 calories per gram of the ignitor. Such values were obtained with the mixture of solid oxygen-oxidizer with NF -containing polymer. In the ignitor mixture, the solid oxygenoxidizer may be coated with a thin coating of compatible solid material, such as saturated polymer, e.g., polyethylene, polypropylene, polyisobutylene, or the like.

The improved binary ignitor of solid oxygen-oxidizer mixed with NF -containing polymer is particularly useful for igniting propellant grains composed of a relatively low proportion of high-energy polymeric binder, e.g., 5 to percent, a high proportion ofa liquid CNF oxidizer, e.g., to 65 percent, a solid oxygen-oxidizer, e.g., 10 to percent, with powdered metal fuel of about I to 10 percent by weight, to obtain a high lsp value above 270, with correspondingly high combustion temperatures above 3,000K. The binders are preferably NF -containing cured polyurethanes and polyacrylates. The liquid CNF oxidizers impart the essentially increased energy and act as plasticizers. They are compounds such as tetrakis(NF butane, tetrakis(NF tetrahydrofuran, hexakis(NF dipropyl ether, and analogous compounds. The solid oxygenoxidizers are of the type indicated to be useful in the ignitor. The metal-containing fuels are powders of boron, beryllium, aluminum, lithium, and their hydrides.

lag and over-pressuring.

No substantial amount of metal fuel is present since metal fuel lowers the effectiveness of the ignitor. Thus, the improved ignitor herein described is a binary mixture of the solid oxygen-oxidizer and the NF containing polymer in close to equal amounts and free of other components, such as liquid oxidizer and metalcontaining fuel. It is to be understood, however, that this binary ignitor may be used with a coating of cement or integument of a cementing polymer to make it adhere to a propellant grain, or may be contained in a plastic bag, such as a polyethylene bag, when used.

By virtue of its low autoignition temperature, in vacuum, the ignitor composed of solid oxygen-oxidizer and NF -containing polymer is very useful in the third stage of a rocket where ignition is required in outer space which is essentially a vacuum. The ignitor could be ignited by a flame-out of the second stage, or by a current pulsing through a resistance wire that contacts with the ignitor and which brings the ignitor up to its ignition temperature in the range of 120C. to about 200C. The ignitor can be applied to the surface of propellant grains of any size or shape to initiate burning at a uniform rate.

The invention described is claimed as follows:

1. An ignitor composition consisting essentially of 40 to wt. percent of a solid oxygen-oxidizer and a solid NF -containing polymer in which NF groups attached to carbon atoms give the polymer an NF content of 40 to 70 wt. percent NF said solid oxygen-oxidizer making available oxygen for reaction with carbon constituents and forming N gas.

2. An ignitor composition consisting essentially of 40 to 70 wt. percent of solid oxygen-oxidizer selected from the group consisting of ammonium perchlorate, hexanitroethane, hydrazine nitroformate, hydrazine perchlorate, hydrazine diperchlorate, and nitronium perchlorate, mixed with 60 to 30 wt. percent of a solid NF containing polymer selected from the group consisting of polybutadiene-NF adduct, NF -containing polyalkyl acrylate, NF -containing polyalkyl ether acrylate, NF containing polyurethane, said polymers containing from 40 to 70 wt. percent NF 3. An ignitor consisting essentially of ammonium perchlorate powder mixed with finely-divided polybutadiene-NF adduct having the composition:

in which the subscript x represents one to two NF groups linked to carbon atoms per recurring monomer unit, the polymer containing in the range of 40 to 70 wt. percent NF 4. The method for improving ignition characteristics of a solid propellant grain which comprises pressing adjacent a surface of the grain to be burned an ignitor composition consisting of 40 to 70 wt. percent of a solid oxygen-oxidizer selected from the group consisting of ammonium perchlorate, hexanitroethane, hydrazine nitroformate, hydrazine perchlorate, hydrazine diperchlorate, and nitronium perchlorate, mixed with 60 to 30 wt. percent of a solid NF -containing polymer which contains 40 to 70 wt. percent NF in carbon-to- NF linkages. 

1. AN IGNITOR COMPOSITION CONSISTING ESSENTIALLY OF 40 TO 70 WT. PERCENT OF A SOLID OXYGEN-OXIDIZER AND A SOLID NF2-CONTAINING POLYMER IN WHICH NF2 GROUPS ATTACHED TO CARBON ATOMS GIVE THE POLYMER AN NF2 CONTENT OF 40 TO 70 WT. PERCENT NF2SAID SOILD OXYGEN-OXIDIZER MAKING AVAILABLE OXYGEN FOR REACTION WITH CARBON CONSTITUENTS AND FORMING N2 GAS
 2. An ignitor composition consisting essentially of 40 to 70 wt. percent of solid oxygen-oxidizer selected from the group consisting of ammonium perchlorate, hexanitroethane, hydrazine nitroformate, hydrazine perchlorate, hydrazine diperchlorate, and nitronium perchlorate, mixed with 60 to 30 wt. percent of a solid NF2-containing polymer selected from the group consisting of polybutadiene-NF2 adduct, NF2-containing polyalkyl acrylate, NF2-containing polyalkyl ether acrylate, NF2-containing polyurethane, said polymers containing from 40 to 70 wt. percent NF2.
 3. An ignitor consisting essentially of ammonium perchlorate powder mixed with finely-divided polybutadiene-NF2 adduct having the composition: (C4H6(NF2)x) in which the subscript x represents one to two NF2 groups linked to carbon atoms per recurring monomer unit, the polymer containing in the range of 40 to 70 wt. percent NF2.
 4. The method for improving ignition characteristics of a solid propellant grain which comprises pressing adjacent a surface of the grain to be burned an ignitor composition consisting of 40 to 70 wt. percent of a solid oxygen-oxidizer selected from the group consisting of ammonium perchlorate, hexanitroethane, hydrazine nitroformate, hydrazine perchlorate, hydrazine diperchlorate, and nitronium perchlorate, mixed with 60 to 30 wt. percent of a solid NF2-containing polymer which contains 40 to 70 wt. percent NF2 in carbon-to-NF2 linkages. 